The Akebono Suprathermal Ion Mass Spectrometer (SMS) is a radio-frequency ion mass spectrometer. It is designed to measure the mass composition and velocity distribution (mass-per-charge, energy-per-charge and angular distribution in the spacecraft spin-plane) of thermal and suprathermal (0.1-4000 eV/q) ions in the ionosphere and magnetosphere. It consists of a retarding potential analyzer, a 3-stage modified Bennett ion mass spectrometer, and a micro-channel plate detector. It can sample ions at 256 mass steps over the 1-80 AMU/q mass range, and 256 retarding potential steps in the 0.1-25.6V range, and 16 suprathermal energy steps in the 100-4000 V range. It operates in a number of fast scan and mass scan operation modes.
For a detailed description of the SMS instrument and its operation, please see Whalen et al, 1990 and Yau et al, 1998.

SMS Summary Plots

The Summary Plots in the SMS SDB present 64-s averaged data (32-s averaged data where an orbit pass is less than 32 minutes), in the following format:

• Panel a: Spin angle versus time spectrogram of thermal H+ ion counts
• Panel b: Spin angle versus time spectrogram of thermal He+ ion counts
• Panel c: Spin angle versus time spectrogram of thermal O++ or He++ ion counts
• Panel d: Spin angle versus time spectrogram of thermal O+ ion counts
• Panel e: Retarding potential steps (histograms) and minimum ram angle
• Panel f: Spin angle versus time spectrogram of suprathermal H+ ion counts
• Panel g: Spin angle versus time spectrogram of suprathermal O+ ion counts
• Panel h: Suprathermal energy steps (histograms) and minimum pitch angle

In panels a-d and g-h:

• The spin angle is defined with respect to the direction nearest to the local magnetic field, in degrees (-180 to 180). 0o ions are parallel to (or closest to) the magnetic field, i.e. downward in the northern and upward in the southern hemispheres. +/-180o ions are anti-parallel to (or farthest from) the magnetic field; +/-90o ions are perpendicular to it.
• The curve denotes the spacecraft ram direction, i.e., the spin angle closest to the spacecraft velocity direction.

In panel d:

• The color of the histogram denotes the instrument entrance aperture selected for the thermal ion measurements. Red: large aperture; yellow: medium aperture; green: small aperture.
• The retarding potential, V, is in volts (0 - 25).
• The minimum ram angle, r, is in degrees (0 - 90).

In panel h:

• The suprathermal energy, E, is in volts (0 - 4000).
• The minimum pitch angle, p, is in degrees (0 - 90).

Data Reliability Flag

• The horizontal line below panel h is a data quality indicator. Green: data valid; yellow: data probably reliable but caution required in data interpretation; red: data may be unreliable - consult SMS Science Team before use; white (or black): data quality unspecified.

If you have any questions or request for the data, please contact DARTS.

Request for using this data

In any publications, the use of the Akebono data should be acknowledged, for example,

“The AKEBONO/SMS data were provided by Prof. Andrew W. Yau through DARTS at the Institute of Space and Astronautical Science (ISAS), Japan”